Xcopy & Secure Folders

I recently installed a RAID 1 Thecus NAS Device on a Network
Initally all the Folders were open but the Customer requested 3 Users have secure Folders which I configured n oproblem
On an evening as an extra backup i use Xcopy to copy the Folders onto another device, this works fine for the open folders but I get "Invalid Drive Spec" when I try to Xcopy the Secure folders across

Is this because only the User has permission to access the said folders